D. c. gas discharge display apparatus with pulse train memory sustaining potential

ABSTRACT

Display apparatus comprises d.c. gas discharge display cells with a sustaining potential thereacross comprising a pulse train with pulse amplitude, pulse duration and pulse spacing such that an ignited cell is reignited upon application of each sustaining pulse and an extinguished cell remains extinguished upon application of the sustaining pulses unless ignited or extinguished by external means.

United States atent n91 Lustig 1 Dec. 11, 1973 1 1 D. C. GAS DISCHARGEDISPLAY APPARATUS WITH PULSE TRAIN MEMORY SUSTAINING POTENTIAL [75]Inventor: Claude D. Lustig, Lexington, Mass.

[73] Assignee: Sperry Rand Corporation, New

York, N.Y.

[22] Filed: Apr. 14, 1972 [21] Appl. No.: 244,011

[52] US. Cl 315/169 R, 315/169 TV [51] Int. Cl. H05b 37/00 [58] Field ofSearch 315/169 R, 169 TV [56] References Cited UNITED STATES PATENTS3/1961 Smith 315/845 4/1971 Mayer et a1 ..315/169R 3,626,241 12/1971 Ngo315/169 R X 3,689,912 9/1972 Dick 315/169 R X 3,600,626 8/1971 Kupsky315/169 R X Primary Examiner-Roy Lake Assistant Examiner-Hugh D. .laegerAtt0rneyl*loward P. Terry 57] ABSTRACT Display apparatus comprises d.c.gas discharge display cells with a sustaining potential thereacrosscomprising a pulse train with pulse amplitude, pulse duration and pulsespacing such that an ignited cell is reignited upon application of eachsustaining pulse and an extinguished cell remains extinguished uponapplication of the sustaining pulses unless ignited or extinguished byexternal means.

7 Claims, 5 Drawing Figures RESERVOlR ADDRESS 1 N6 Cl RCUlTY MEMORYPULSE SOURCE PATENTEDDEB 11 ms 37 95 PLASMA RESERVOIR/W ADDRESSINGcmcuwv HIO ME-MORY PULSE SOURCE PATENIEUUEE 11 ms ELECTRON ELECTRONDENSITY CURRENT DENSITY VOLTAGE CURRENT 3778.674 SHEET 3 (IF 3 V3ORV3 YI I ELECTRON DENSITY I Y |N LIT CELLS P X 36 I I- AMBIENT ELECTRON IDENSITY IN [1 n UNLIT CELLS AMBIENT ELECTRON DENSITY IN UNLIT CELLS D.C. GAS DISCHARGE DISPLAY APPARATUS WITH PULSE TRAIN MEMORY SUSTAININGPOTENTIAL BACKGROUND OF THE INVENTION 1. Field of the Invention Theinvention pertains to d.c. gas discharge display apparatus, particularlywith regard to the memory sustaining potential thereof.

2. Description of the Prior Art D.C. gas discharge display devices areknown in the prior art that include a plurality of gas discharge displaymemory cells. Conventionally, a dc. gas discharge sustaining potentialof amplitude intermediate the ignition and extinction potentials of thecell gas discharges is applied across the array of memory cells. Thus,whenever a discharge is selectively ignited in a cell, the cell remainsignited thereby providing memory. Similarly, a cell once extinguishedremains extinguished until selectively reignited. One type of such gasdischarge display apparatus is known in the art as the x-y addresseddisplay panel. In such devices, a plurality of anodes are disposedorthogonally with respect to a plurality of cathodes, the intersectionsthereof forming an x-y grid. The d.c. sustaining potential is appliedbetween all of the cathodes with respect to all of the anodes. Toselectively ignite a cell, the potential is increased at a selectedx-electrode and at a selected y-electrode such that only the potentialat the intersection of the selected electrodes exceeds the firingpotential of the gas, thus igniting a discharge at the selected cell.When the increased potentials are removed, the sustaining potentialmaintains the discharge ignited. A similar procedure is utilized inextinguishing an ignited cell by reducing the potentials on a selected xand a selected yelectrode.

D.C. gas discharge display panels having a plurality of memory cellswith d.c. sustaining potential thereacross may also ignite selectedmemory cells by selectively applying preionization thereto. Examples ofsuch displays are described in US. patent application Ser. No. 90,538filed Nov. 18, 1970 entitled Digitally Addressable Gas Discharge DisplayApparatus by Claude D. Lustig and Albert W. Baird III and US. Pat.application Ser. No. 161,584 filed July I2, 1971 entitled Gas DischargeDisplay Apparatus by Theodore H. Bonn, both assigned to the assignee ofthe present invention.

It has been found with such display panels that when reasonablesustaining potentials are applied across the memory cells, arcingbetween the cell electrodes frequently occurs reslting in displayinstability or damage to the devices. A prior art solution to thisinstability problem has been to utilize a resistor in series with eachof the display cell discharges thus limiting the current flow and henceprecluding arc formation In many applications of such panels, it isfrequently desirable to utilize large arrays of display memory cells. Insuch panels, the inclusion of a large number of individual resistorsresults in substantial constructional difficulties. Furthermore, it isnot possible to utilize a single resistor in series with an array ofcells, since the current drawn by igniting several cells results in avoltage drop across the series resistor thus reducing the sustainingvoltage appearing across the array of cells. Hence, increasingdifficulty is encountered when attempting to ignite larger numbers ofcells. This voltage dependence on the number of cells ignited causesfurther display instabilities.

Because of the attendant difficulties in designing a stable large-scaled.c. gas discharge display panel with memory, practitioners in the artturned their attention to ac. display panels, a wide variety of whichare known in the art. In such panels, the electrodes are electricallyinsulated from the gas plasma thus preventing arc instabilities. It wasdiscovered, however, that the ac. panels are constructionally morecomplicated than the d.c. panels thus resulting in higher manufacturingcosts for the a.c. display devices. Additionally, the a.c. panelsrequire somewhat larger potentials than do the d.c. panels thuscomplicating the attendant panel circuitry and again increasing the costthereof. In addition, the ac. display panels are not normally compatiblewith some of the simple d.c. addressing arrangements developed for thed.c. type of panels. Such a simple d.c. addressing arrangement isdisclosed in said Ser. No. 90,538.

SUMMARY OF THE INVENTION The present invention provides a stable d.c.panel display with memory in which are formation is prevented withoutthe use of resistors in series with the gas discharges by utilizing apulse train sustaining potential. The pulse amplitude, pulse durationand pulse spacing are selected such that a cell once ignited iscontinuously reignited by the sustaining pulses and a cell onceextinguished remains extinguished during the application of thesustaining pulses. The duration of the pulses is sufficiently narrow andthe spacing between the pulses is sufficiently wide such that areformation is prevented. Thus, it is appreciated that with the d.c.sustaining potentials of the prior art devices, when substantial currentsurges develop, an arc may be formed causing damage to the displaydevice and the associated circuitry. Utilizing the pulse trainsustaining potential of the invention, the sustaining voltage pulse istoo narrow to permit an arc to develop. Thus, the invention providesgreater display stability without utilizing series resistors andparticularly for large scale arrays of memory cells. I

An attendant advantage of the invention is that less operating power isrequired and hence less power dissipation and heat generation occurs ingas discharge devices utilizing the invention as compared to the priorart d.c. arrangements, including those which do not incorporate seriesresistors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of aportion of a gas discharge display panel suitable for incorporating inthe invention.

FIG. 2 is a sectional elevation view of the panel of FIG. 1 taken alongthe line 2-2 of FIG. 1.

FIG. 3 is a current-voltage characteristic curve of a typical coldcathode gas discharge utilizing d.c. excitation.

FIG. 4 is a waveform diagram illustrating waveforms useful in explainingthe operation of the invention.

FIG. 5 is a current-voltage characteristic curve of a cold cathode gasdischarge utilizing pulsed excitation in accordance with the invention.

DESCRlPTlON OF THE PREFERRED EMBODIMENT Referring to FlG. 1, a portionof a gas discharge display panel suitable for incorporating theinvention and of the type described in said Ser. No. 90,538 isillustrated. Since the structure and operation of such a display panelis discussed in detail in said Ser. No. 90,538, only a concisedescription thereof will be given here for brevity.

The apparatus includes a display memory section comprising a pluralityof gas discharge display cells. Adjacent to the display section 10 are astack of ad dressing electrodes ll, only the last addressing anode 12 inthe stack 11 being illustrated. Adjacent to the stack of addressingelectrodes i1 is a gas plasma reservoir not shown herein for simplicity.

The display section 10 of the panel includes a display anode structure13 which may, for convenience, com prise a metal plate with a matrix ofapertures therethrough. The display section 10 also includes a cathodestructure 14 which may be instrumented by a metal plate with a matrix ofapertures therethrough in a manner similar to the cathode plate 13. Aninsulator plate 15, having a matrix of apertures therethrough, isdisposed between the plates l3 and 14. A transparent face plate 16,through which a display pattern may be viewed, is also included in thedisplay section 10. Two perforated insulated plates 17 and 18 aredisposed between the cathode plate 14 and the transparent face plate 16to inhibit sputtering of material from the cathode plate 14 to the faceplate 16, which sputtered material would tend to obscure the display.

A perforated insulator plate 19 is interposed between the display anodeplate 13 and the addressing anode l2. lt will be appreciated that theplates 12-.19 are disposed adjacent one another in stacked arrangementwith the matrices of apertures through the respective plates aligned toform gas conductive channels and sealed around the edges to form a gastight structure in the manner described in said Ser. No. 90,538.

Addressing circuits 2% are included for selectively applying potentialsto the portions of the addressing anode plate 12 as well as to theportions of the remaining addressing anode plates of the addressingstack 11 in the manner described in detail in said Ser. No. 90,538.

The apparatus of FIG. 1 also includes memory pulse source circuits 25.The circuits 25 apply a sustaining pulse train waveform between thedisplay anode plate 13 and the display cathode plate 1d in accordancewith the concepts of the invention in a manner to be described.

It will be appreciated that the display anode plate 13 and the displaycathode plate 14 together with the insulator plate define a plurality ofgas discharge display cells in the manner described in said Ser. No.90,538. For example, the aperture 26 in the insulator plate 35 defines agas discharge cell whose anode and cathode electrodes are provided bythe portions of the plates 13 and 14 adjacent the aperture 26,respectively.

With the memory pulse source circuits 25 providing a sustaining voltagepulse train waveform between the display electrodes 13 and 14 in amanner to be described in accordance with the invention, a display cellof the memory section 10 is selectively ignited in the manner describedin detail in said Ser. No. 90,538. The

manner in which a memory cell is ignited will be explained brieflyherein for completeness. With appropriate addr'essing potentials appliedby the addressing circuits 24 to the portions of the anodes of theaddressing stack lll, a gas plasma column will be extended from theplasma reservoir to impinge upon a selected aperture in the addressinganode 12. For example, when the aperture 27 is addressed through thestack of electrodes iii, a gas plasma column 30 is extended from thereservoir to impinge upon the aperture 2'7 and then through to theaperture 28 in the display cathode plate 13. Since the sustainingvoltage pulse train is applied between the display electrodes 13 and 14,a gas discharge is ignited in the memory cell 26 by the ionizationintroduced thereat by the plasma column 30. when the addressingpotentials from the circuits 24 are removed, thus terminating theapplication of the plasma column 30 to the aperture 28, the display.cell 26 remains ignited because of the sustaining action of the pulsetrain provided by the circuits 25 in a manner to be described Thus itwill be appreciated that an information pattern may be displayed by thememory section 10 by selective ignition of the display cells thereof. Adisplayed pattern may be erased by momentarily removing the sustainingpotential waveform from the electrodes 13 and M.

Referring to FIG. 2, in which like reference numerals indicate likecomponents with respect to FlG. 1, an elevation view taken in sectionalong the line 22 of FIG. 1 is illustrated to further aid inunderstanding the construction and arrangement of the elements of FIG.1.

A cold cathode gas discharge normally requires a lower voltage tosustain the discharge than is required to ignite it. A sustainingvoltage applied to an array of gas discharge cells will not causeignition of any of the cells until a voltage higher than the sustainingvoltage is applied to selected cells or until the firing voltage ofselected cells is lowered, for example, by local preionization. Thecells in the array have memory in the sense that the cells will remainlit after the original ignition instrumentations, e.g., the highervoltage pulse or the preionization, are removed.

Referring to FlG. 3, the current-voltage characteristic of a typicalcold cathode d.c. gas discharge is illustrated. Point P represents atypical operating condition with a sustaining voltage which may beapplied from a sustaining voltage source through a resistor in serieswith the discharge as indicated by the legend V Alternatively, thesustaining voltage V may be applied from a voltage source without aseries resistor as indicated by the legend V Operation without a seriesresistor is necessary if many display cells are to be sustained from thesame power supply to avoid variations in cell voitages as differentnumbers of cells are ignited. Memory is obtained because the voltageacross a cell must be increased to V before ignition occurs. Once a cellhas been ignited it can be sustained with a lower voltage, for example Vbecause strong space charge fields are established at the cell cathodeincreasing its emission efficiency.

It will therefore be appreciated that in prior art d.c. gas dischargedisplay panels, i.e., panels having the cell electrodes in contact withthe discharge and operated with d.c. potentials, a d.c. sustainingpotential is conventionally applied across the display cells so as toeffect the memory function. As previously discussed, the use of a d.c.sustaining potential has attendant disadvantages. Therefore, inaccordance with the invention, the memory pulse source 25 of FIG. 1provides a pulse train as illustrated in FIG. 4a with pulses of durationt, amplitude V and spacing T. This pulse train sustaining waveform, asillustrated in FIG. 4a, is applied between the anode plate 13 and thecathode plate 14 of the display cells of FIG. 1. It will be appreciatedthat circuits for providing pulse trains such as that of FIG. 4a arewell known in the art and will not be further described for brevity.

with the pulse train sustaining waveform of FIG. 4a applied across thememory cells 10 of FIG. 1, the electron density of lit cells may followa curve 35 as illustrated in FIG. 4b and the electron density of unlitcells may not rise above the level 36 as further illustrated in FIG. 4b.Thus, in lit cells when breakdown occurs during the application of asustaining pulse of duration t, the electron density within the cellincreases to a relatively large value and decays during the timeinterval T between voltage pulses to a minimum value Y. When theelectron density decays to the point Y, the next sustaining pulseoccurs, again firing the cell and increasing the electron densitytherein to a large value. It will be appreciated that the parameters ofthe pulse sustaining waveform of FIG. 4a must be chosen such that theelectron density in lit cells remains sufficiently high between pulsesso as to continuously reignite the cells upon application of each of thesustaining pulses. In unlit cells, however, the parameters of the pulsetrain sustaining waveform of FIG. 4a are chosen such that the electrondensity within the unlit cells remains below a point X which issignificantly lower than point Y. Thus in unlit cells, the electrondensity does not achieve a value such that the sustaining pulses canproduce ignition therein. FIG. 40 illustrates the current drawn by litcells during application of the sustaining pulse train of FIG. 4a.

Thus, it is appreciated that memory is obtained because the duration 1of the applied voltage pulses is chosen to be sufficiently short thatthe pulses will cause ignition only in cells which were lighted duringthe previously occurring pulse, since the electron density therein isrelatively high. In addition the interval T between pulses is selectedto be sufficiently short so that the electron density at the times thevoltage pulses are applied is still appreciably higher than the ambientelectron density in cells which have not been ignited, as illustrated bypoints Y and X, respectively, of FIG. 4b.

Referring to FIG. 5, a dc. current-voltage gas discharge characteristicsimilar to that shown in FIG. 3 is illustrated. When the pulse trainsustaining voltage of FIG. 4a is of amplitude V an operating conditionof point Q is established. Should the pulse train sustaining waveformamplitude be V then an operating condition of point Q will beestablished. It is appreciated that the pulse amplitudes V or V arenormally chosen near the firing potential V of the gas discharge. Thepeak voltages V;, or V may be substantially below or above Vrespectively, depending upon the values of t and T. For large values ofT and small values oft an amplitude V will normally be chosen above Vand for small values of T and large values of t, a peak voltage V willnormally be chosen below the firing potential V Choices of: and T willdepend on the gas composition of the discharge since breakdownconditions and electron density decay rates vary as a function of thegas composition. It will be appreciated that the peak voltages V or Vmay take on a wide range of values less than, equal to and above thefiring voltage V of the gas.

The pulse train sustaining waveform of FIG. 4a will not by itself causeignition. In order to ignite a selected cell, either ionization isintroduced to raise the ambient electron density level X to the level Y(FIG. 4b) or alternatively, one or more of the sustaining voltage pulsesis increased in amplitude or width or both. The former cell ignitionmethod would be utilized with display panels of the type described insaid Ser. No. 90,538 or said Ser. No. 161,584 by the methods describedtherein. The latter ignition method would be utilized in X-Y addressedpanels of a type known in the art where the amplitude or width of thesustaining pulses on an X conductor as well as on a Y conductor would beincreased to cause ignition selectively at the cell located at theintersection of the conductors. A cell may be erased in an X-Y addressedpanel by decreasing the sustaining potentials at selected X and Yconductors in order to decrease the potential at the intersectionsthereof to below the extinction voltage of the discharge. In panels ofthe type illustrated in said Ser. No. 90,538 or said Ser. No. 161,584,the cells may be erased by momentarily disrupting the application of thesustaining pulse train.

It will be appreciated that the principles of the invention may beapplied to a wide variety of display panel configurations with a widevariety of parameters selectable for the puse train sustainingpotential. Once the principles of the invention as explained above areunderstood, the dimensions of the display panels and the parameters ofthe pulse train sustaining waveform may be chosen in accordance with thewell known gas discharge laws.

For example, a gas discharge display panel that provides satisfactoryoperation is designed as follows. With reference to FIGS. .l and 2 thecathode I4 is a 0.005 inch thick nickel-iron alloy plate with a square32 X 32 array of apertures 0.014 inches in diameter with a 0.031 inchcenter-to-center spacing. The anode plate 13 is similar in constructionto the cathode plate 14 with the exception that the aperture diametersare 0.010 inches. The anode plate 13 and the cathode plate 14 areseparated by a glass sheet 15 wich is 0.006 inches thick with 0.018 inchdiameter apertures therethrough. Two identical perforated glass sheets17 and 18 separate the cathode plate 14 from the front glass cover plate16 to reduce sputtering.

Such a panel filled with neon and mercury vapor at torr pressureoperates properly with a pulse train sustaining waveform with V3=205volts, t=2 microseconds and T=14 microseconds. The operating currentwaveform for such a configuration is illustrated in FIG. 30. Since the(1.0. firing voltage V for this panel is 210 volts, the value of V;., of205 volts demonstrates operation with the amplitude of the sustainingpulses below V Operational parameter measurements were made on thispanel with regard to average power dissipation per cell, display cellmemory margin, and display cell uniformity; where memory margin is ameasure of the difference between the voltage pulse amplitudes requiredto fire and extinguish the array of cells and uniformity is a measure ofthe range of extinction voltage pulse amplitudes with regard to thearray of cells. It was found, for the above-described panel, that theaverage power dissipation per cell was about one-half that required fora dc. sustaining potential applied without series resistance. The memorymargin for the cells was slightly less than that obtainable with a dcsustaining potential but was significantly greater than that obtainedwith a typical prior art ac. plasma display panel. The cell uniformityfor the above'described panel was found to be satisfactory for operationin practical applications of the invention.

The above-described panel was also operated with a pulse trainsustaining waveform having V =220 volts, [=2 microseconds and T 2lmicroseconds. Since, as previously described, the dc. firing voltage Vis 210 volts, the value of V demonstrates operation with the amplitudeof the sustaining pulses above V A memory margin was obtained similar tothat of the device utilizing the previously described pulse trainsustaining waveform.

In a somewhat different operating mode, waveforms such as thoseillustrated in H6. 4 (d and e) are also obtainable when utilizing asustaining waveform with increased pulse duration and spacing ascompared to that previously described, for example with i=4 microsecondsand T=4O microseconds. In this mode the gas takes longer to break downand the effective duty cycle and, hence, power dissipation are furtherreduced as compared to a dc. sustaining potential by about a factor of3. However, the memory margin obtained under this condition isconsiderably lower.

Results similar to those described above are also ob tained with Penningmixture (for example, 99.5 percent neon and 0.5 percent argon) andmercury vapor at 100 torr pressure. However, under pulsed conditions inaccordance with the invention a greater memory margin can be providedthan is obtainable with a dc. sustaining voltage. This is because theshort voltage pulse durations do not allow the formation of anappreciable density of metastable neon atoms on which the Penningeffect, i.e., the ionization of argon atoms by collision with metastableneon atoms, depends. Thus under pulsed conditions the firing voltage isdisproportionately high, resulting in an increased memory margin. Forexample, with t=l microsecond and T=8 microseconds a memory margin,defined as %(V;V )/V;, of 0.5 is obtained, relative to a value of 0.35under dc. sustaining voltage conditions. it will be appreciated thatother gas compositions which exhibit the penning effect may also beutilized in practicing the invention to obtain the increased memorymargin compared to do. operation as described above.

The afore-described embodiments of the invention have been described interms of particular ionizable gases. It will be appreciated that a widevariety of suitable ionizable gases are available for use in practicingthe invention.

It will be appreciated from the foregoing that the present inventionprovides substantially increased stability against arc formation forplasma displays without resistors in series with the discharges. When asubstantial current surge develops in prior art d.c. devices, an arc canbe initiated causing damage to the device and the associated circuitry.In the pulsed memory mode of the present invention, the sustainingpulses are too short to permit an arc to develop. Furthermore, the slopeof the curve of average current versus voltage is less for the pulsedmode of operation than the slope of the dc. voltagecurrent curve whichalso improves the stability without requiring series resistors.

The present invention provides lower operating power and hence lesspower dissipation and heat loss in the gas discharge device as comparedto the prior art configurations. Although the peak currents and thevoltages associated with the gas discharge sustaining function of thepresent invention may be higher than in the prior art dc. voltagesustaining situation, the low duty cycle of the pulsed mode waveformprovides a net power reduction even compared to the minimum d.c.sustaining potential required to provide memory in a givenconfiguration. This is particularly important for high resolutiondevices which may contain a high density of cells operating at high peakcurrents. It is furthermore appreciated that the present inventionprovides the possibility for dimming the display. The cell brightnessmay be varied by altering the duty cycles of the applied sustainingvoltage waveforms.

While the invention has been described in its preferred embodiments, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes within the purviewof the appended claims may be made without departing from the true scopeand spirit of the invention in its broader aspects.

1 claim:

I. In d.c. gas discharge display apparatus display cathode means,

display anode means,

said display cathode means and said display anode means defining d.c.gas discharge memory cell means for containing an ionizable gas,

said cathode and anode means being internal to said cell means and incontact with said gas, and

pulse soure means coupled without any discharge current limitingresistors to said cathode and anode means for applying a gas dischargesustaining pulse train therebetween, the pulses thereof being of suchamplitude and duration and the spacing between said pulses being suchthat an ignited memory cell is reignited and an extinguished memory cellremains extinguished upon application of said pulses.

2. ln d.c. gas discharge display apparatus display cathode means,

display anode means,

said display cathode means and said display anode means defining d.c.gas discharge memory cell means for containing an ionizable gas, saidcathode and anode means being internal to said cell means and in contactwith said gas,

addressing means for extending gas discharge columns to selected memorycells thereby increasing the level of ionization therein, and

pulse source means coupled without any dicharge current limitingresistors to said cathode and anode means for applying a gas dischargesustaining pulse train therebetween, the pulses thereof being of suchamplitude and duration and the spacing between said pulses being suchthat a selected memory cell is ignited by said sustaining pulses in thepresence of said increased level of ionization from said extended columnand is reignited upon application of subsequent pulses and extinguishedmemory calls remain extinguished upon application of said pulsesv tion.

6. In the apparatus of claim 5 in which said ionizable gas comprises apenning mixture.

7. In the apparatus of claim 2 in which said pulse source means includesmeans for providing said sustaining pulse train, the pulses thereofbeing of such amplitude and duration and the spacing between said pulsesbeing such that less net sustaining power is required with respect toutilizing a minimum possible d.c.

sustaining potential.

Notice of Adverse Decision in Interference In Interference No. 98,614,involving Patent No. 3,77 8,674, C. D. Lustig, DC. GAS DISCHARGE DISPLAYAPPARATUS WITH PULSE TRAIN MEMORY SUSTAINING POTENTIAL, final judgmentadverse to the patentee was rendered Apr. 30, 197 5, as to claims 1, 2,3, 4, 5, 6 and 7.

[Oyficz'al Gazette August 5,1975]

1. In d.c. gas discharge display apparatus display cathode means,display anode means, said display cathode means and said display anodemeans defining d.c. gas discharge memory cell means for containing anionizable gas, said cathode and anode means being internal to said cellmeans and in contact with said gas, and pulse soure means coupledwithout any discharge current limiting resistors to said cathode andanode means for applying a gas discharge sustaining pulse traintherebetween, the pulses thereof being of such amplitude and durationand the spacing between said pulses being such that an ignited memorycell is reignited and an extinguished memOry cell remains extinguishedupon application of said pulses.
 2. In d.c. gas discharge displayapparatus display cathode means, display anode means, said displaycathode means and said display anode means defining d.c. gas dischargememory cell means for containing an ionizable gas, said cathode andanode means being internal to said cell means and in contact with saidgas, addressing means for extending gas discharge columns to selectedmemory cells thereby increasing the level of ionization therein, andpulse source means coupled without any dicharge current limitingresistors to said cathode and anode means for applying a gas dischargesustaining pulse train therebetween, the pulses thereof being of suchamplitude and duration and the spacing between said pulses being suchthat a selected memory cell is ignited by said sustaining pulses in thepresence of said increased level of ionization from said extended columnand is reignited upon application of subsequent pulses and extinguishedmemory calls remain extinguished upon application of said pulses.
 3. Inthe apparatus of claim 2 in which said pulse source means includes meansfor providing said pulses with amplitudes less than the firing potentialof said ionizable gas.
 4. In the apparatus of claim 2 in which saidpulse source means includes means for providing said pulses withamplitudes at least as great as the firing potential of said ionizablegas.
 5. In the apparatus of claim 2 in which said ionizable gascomprises a gas exhibiting the penning effect, for increasing the memorymargin of said memory cell means with respect to d.c. sustainingpotential operation.
 6. In the apparatus of claim 5 in which saidionizable gas comprises a penning mixture.
 7. In the apparatus of claim2 in which said pulse source means includes means for providing saidsustaining pulse train, the pulses thereof being of such amplitude andduration and the spacing between said pulses being such that less netsustaining power is required with respect to utilizing a minimumpossible d.c. sustaining potential.